The head of Ukraine's emergency services has said his workers have been chased away from the MH17 crash site by pro-Russian rebels.

Speaking to journalists at a news conference in Kharkiv, Serhiy Bochkovskiy said emergency services personnel also had some of their equipment confiscated.

Jan Tuinder: 'You call them terrorists; to me it's criminal'

Mr Bochkoskiy added his workers did not open body bags when they prepared them to be removed and that the transportation of victims' remains was done in "a very proper way".

When asked how difficult the work was, he replied: "We are human beings, we are made of flesh and blood, not of steel and stone. So when we work with those remains, the remains of human beings, we are both sad and angry."

Video:Australian Service For MH17 Dead

Also speaking was Jan Tuinder, a forensics expert with the Dutch National Police who said it had been hard for investigators to gain access to some of the bodies.

"There are still some lunatics, it's very hard for us to get to the bodies, to get to the remains," he said.

"They are moving away from the main crash zones where the landing gear and cockpit came down," she said. "Much of that is wedged hard into the ground and has melted because of the massive fire that broke out.

"They are being accompanied everywhere they go by separatist gunmen - most of whom are from the Berkut pro-Russian special forces.

"They are very heavily armed and have their guns with the safety catch off."

OSCE investigators working at the Farnborough headquarters of the Air Accidents Investigation Branch are continuing to work on the plane's cockpit voice recorder and the flight data recorder.

Investigators say the data has been retrieved and there was no evidence the recorder was tampered with.

:: Ukraine's Prime Minister Arseniy Yatsenyuk resigned on Thursday after two parties declared they would pull out of the governing coalition. Yatsenyuk said Parliament could no longer do its work and pass necessary laws.

His departure will pave the way for elections that will reflect the country's changed political landscape after the removal of pro-Russian President Viktor Yanukovych in February.

The United States has said that Russia was firing artillery across the border into Ukraine to target Ukrainian military positions in its conflict with pro-Russian separatists.

"We have new evidence that the Russians intend to deliver heavier and more powerful multiple rocket launchers to the separatist forces in Ukraine, and have evidence that Russia is firing artillery from within Russia to attack Ukrainian military positions," said State Department spokeswoman Marie Harf.